The present invention relates to compositions and methods for converting chrysotile and/or amosite asbestos-containing matrices, such as thermal insulation materials, found on pipes or other metal surfaces, to non-regulated environment benign materials and for preventing the corrosion of the pipes or other metal surfaces.
Asbestos is a commercial term applied to a group of silicate minerals which occur in fibrous form. There are six principal asbestos minerals. Of these six minerals, only one, chrysotile asbestos, belongs to the group classified as serpentine asbestos, that is, minerals characterized by long fibers which are serpentine in shape. The chemical composition of chrysotile asbestos may be represented as: Mg.sub.3 (Si.sub.2 O.sub.5)(OH).sub.4 or 3MgO.multidot.2SiO.sub.2 .multidot.H.sub.2 O. The crystalline structure of chrysotile asbestos consists of alternating layers of silica and magnesium oxide/hydroxide bound to each other through covalently shared oxygen. These layers are transverse to the fiber axis.
The other varieties of asbestos are typically silicates of magnesium, manganese, iron, calcium and sodium. These varieties of asbestos belong to the amphibole (straight fiber) group of minerals. The amphibole's fundamental unit is a chain of SiO.sub.4 tetrahedra linked by comer oxygen atoms, and the chains are linked laterally by cations, such as Mg, Mn, and Fe. Grunerite asbestos, more commonly referred to as amosite, is one of the most readily available and commercially used varieties of the amphibole group of minerals. The chemical composition of amosite asbestos may be represented as: Fe.sub.7 Si.sub.8 O.sub.22 (OH).sub.2.
Although about 90% of the world production is the chrysotile form of asbestos, amosite is widely used in high-temperature insulation, acid-resistant products and asbestos cement. Particularly, amosite is used as high-temperature insulation around iron and other metal pipes and surfaces. Iron may include iron alloys such as alloys with cobalt, nickel, chromium, manganese, carbon, including steel and stainless steel. Other metals used in .pipes may include copper, aluminum, brass, zinc or any other commonly used metal for piping or building construction.
For a number of years now it has been recognized that many chronic diseases are associated with the inhalation of airborne asbestos fibers, including both chrysotile and amosite asbestos. These diseases include lung cancer, chronic fibrosis of the lung lining, and mesothelioma, a rare but fatal cancer of the lungs.
Government agencies have passed regulations banning the use of products containing either chrysotile or amosite asbestos in building construction. However, asbestos-containing materials are still present in many structures built before the regulations went into effect and remain a potential health threat. Building owners have used various methods to address the dangers posed by asbestos and to ensure that asbestos fibers do not enter occupied space. One temporary and relatively inexpensive method is encapsulation, where the asbestos-containing materials are sprayed with a surface-coating material to seal-in the asbestos. This method, however, provides only a temporary remedy since the asbestos fibers are only isolated by the encapsulation. Moreover, merely encapsulating asbestos covered pipes will not prevent exposure when a pipe bursts or the integrity of the encapsulation is otherwise compromised.
Thus, another method employed by building owners is the complete removal of all chrysotile and/or amosite asbestos-containing materials. The drawback to this method is that it involves a significant amount of time and expense because a building must be sealed off, the asbestos-containing materials removed (usually by hand to minimize the dust), and once removed, the asbestos-containing materials must be disposed. In addition, many safeguards must be employed to prevent inhalation of airborne asbestos by workers and others in the vicinity of the working area and government regulations often require the continuous monitoring of the air while the work is being done. Furthermore, because of the hazardous nature of the asbestos-containing material that is removed, the disposal is very costly.
A number of methods have been proposed for rendering asbestos-containing material less harmful. U.S. Pat. Nos. 5,041,277 and 5,258,562, both to Mirick, and U.S. Pat. No. 5,264,655 to Mirick, et al. are directed to methods and products for converting asbestos to a non-asbestos material. The method disclosed in the '277 patent requires wetting the asbestos-containing materials with weak organic acids and subsequently rewetting the asbestos-containing materials with additional weak organic acids. This method, although substantially effective, is not efficient in time and cost because it requires successive wetting of asbestos-containing materials.
The methods ofthe '562 patent and the '655 patent require wetting asbestos-containing material with an aqueous solution consisting of weak organic acid, such as trifluoroacetic acid, and optionally fluoride ions. The methods of the Mirick and Mirick, et al. patents contemplate soaking the asbestos-containing material when possible or spraying the asbestos-containing material when the methods must be employed in situ. Although the methods of the Mirick and Mirick et al. patents may be effective, they are not efficient in cost and time, especially when the in situ spraying method is used, because the disclosed technology requires the conversion process to be repeated as frequently as possible so that the asbestos-containing materials are subjected to successive spraying with acid solution.
As amosite asbestos is used mainly in high-temperature insulation, acid-resistant products and asbestos cement, it has been widely used to insulate pipes, furnaces, boilers and other metal surfaces, which generally require an in situ treatment. Consequently, any in situ method for chemically converting the amosite asbestos to environmentally benign materials must take into account the effect of the chemicals on the metal pipes, boilers and other metal surfaces. Many of the known asbestos treatment methods use acids, such as sulfuric, hydrochloric, nitric, phosphoric, formic, acetic or other weak organic acids, alone or sometimes in combination with metal or acidic salts. Moreover, these known methods often call for treatment at elevated temperatures. While these known methods may be effective in treating asbestos, the conditions under which they are used will likely cause rapid corrosion of most commonly used metals found in building construction, especially iron and carbon steel. Thus, there is a need for a chemical reagent that converts the asbestos-containing materials to non-regulated environmentally benign materials and also inhibits the corrosion of the pipes and other metal structures that are covered by the asbestos insulation.